properties of sea ice (vish)
TRANSCRIPT
PROPERTIES OF SEA ICE
PROPERTIES OF SEA ICE
SALITY
DENSITY
SPECIFIC HEAT
LATENT HEAT OF FUSION
LATENT HEAT OF FREEZING
VAPOR PRESSURE OF SEA ICE
LATENT HEAT OF EVAPRATION
COEFFICIENT OF THERMAL EXPANSION
COEFFICIENT OF THERMAL CONDUCTIVITY
LAY OUT
The properties of sea ice depend upon the salinity of sea water from which it forms , temperature , air-content or porosity , pressure , speed of ice formation , age and history of the ice.
On further cooling the various salts present in the sea water crystalize gradually depending upon the temperature.
Example :-
sodium sulphate crystalize at -36 0c
calcium chloride crystalize at -55 0c
Properties of sea ice
The salinity of the sea ice depends upon the salinity of the original sea water ,the speed of the ice formation and the age of the ice.
Sea ice less than the salinity of the original sea water. Because some portion of the brine between the ice crystals seeps out.
The salinity of the sea ice varies in old ice.
Salinity of sea ice decreases with increasing thickness of the ice sheet because the process of ice formation is slower below thicker ice sheet.
salinity
The density of sea ice depends mainly on it’s air-content or porosity , the amount of enclosed brine and the freezing temperature.
rt = (1-a) (1+4.56 S / T) 0.917
r – density of the sea ice in g/cm3
a – air-content volume %
S – salinity in ppt
T – temperature in 0c .
DENSITY
While pure water in the liquid state has a density of 0.999867 at 0c.
The density of sea ice varies both above and below that of pure ice , above and below 0.91676 depending upon the brine content in the ice and air content.
Cont….
The specific heat of pure ice depends upon it’s temperature.
It depend upon the salt content and temperature of the sea ice.
The specific heat of pure ice is less than half that of pure water.
Specific heat = salinity of the water.
The specific heat of sea ice is higher than the specific heat of pure ice. Because more amount of specific heat required for melting or freezing of additional salt content in sea ice.
SPECIFIC HEAT
The latent heat of fusion pure ice the heat required to melt pure nice at o0c and at atmospheric pressure is 79.67 cal /g .
Melting of sea ice does not occur at a fixed temperature due to the presence of salts.
Definition of the latent heat of fusion as the amount of heat required to melt 1g of sea ice of given salinity that was initially at the indicated temperature.
Latent heat of fusion
The vapor pressure of sea ice has not been investigated but it cannot depart very much that of pure ice , which has the following values :
0c e
o0 6.11 mb
-10 0 2.61 mb
-20 0 1.04 mb
-30 0 0.39 mb
Vapor pressure of sea ice
The ice can volatize directly to vapor without going through the liquid stage in which case the latent heat of evaporation is about 600 calories / g .
If the evaporation proceeds more slowly , the ice melts before vaporizing and 700 calories / g are required.
The later process seems to prevail in nature.
Latent heat of evaporation
For pure ice the coefficient of thermal expansion (e) per one degree is about 1.7 * 10 -4.
The coefficient is independent of temperature.
The thermal expansion of sea ice is a function of temperature and salinity and shows a considerable range overboth positive and negative values. The negative values indicate expansion on cooling , positive values contraction of cooling.
The coefficient decreases at lower temperatures but is always negative.
Coefficient of thermal expansion
The coefficient of thermal conductivity of pure ice is about 0.005 which approximately three times great as of pure water at o0 .
The conductivity was greatly affected by the character of the ice , particularly by the gas content of the ice.
In natural the porosity is greater near the surface than in deeper portions of the ice.
On avg the coefficient of thermal conductivity near the surface was about 1.5 * 10 -3 at 0.5m it was 4 *10 -3 and below 1m , the pure ice given above namely 4* 10 -3.
Coefficient of thermal conductivity
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